A new method for producing clean hydrogen

May 23, 2013

Duke University engineers have developed a novel method for producing clean hydrogen, which could prove essential to weaning society off of fossil fuels and their environmental implications.

While hydrogen is ubiquitous in the environment, producing and collecting molecular hydrogen for transportation and industrial uses is expensive and complicated. Just as importantly, a byproduct of most current methods of producing hydrogen is carbon monoxide, which is toxic to humans and animals.

The Duke engineers, using a new catalytic approach, have shown in the laboratory that they can reduce carbon monoxide levels to nearly zero in the presence of hydrogen and the harmless byproducts of carbon dioxide and water. They also demonstrated that they could produce hydrogen by reforming fuel at much lower temperatures than conventional methods, which makes it a more practical option.

Catalysts are agents added to promote chemical reactions. In this case, the catalysts were nanoparticle combinations of gold and iron oxide (rust), but not in the traditional sense. Current methods depend on gold nanoparticles’ ability to drive the process as the sole catalyst, while the Duke researchers made both the iron oxide and the gold the focus of the catalytic process.

“Our ultimate goal is to be able to produce hydrogen for use in fuel cells,” said Titilayo “Titi” Shodiya, a graduate student working in the laboratory of senior researcher Nico Hotz, assistant professor of mechanical engineering and materials science at Duke’s Pratt School of Engineering. “Everyone is interested in sustainable and non-polluting ways of producing useful energy without fossil fuels,” said Shodiya, the paper’s first author.

Fuel cells produce electricity through chemical reactions, most commonly involving hydrogen. Also, many industrial processes require hydrogen as a chemical reagent and vehicles are beginning to use hydrogen as a primary fuel source.

“We were able through our system to consistently produce hydrogen with less than 0.002 percent (20 parts per million) of carbon monoxide,” Shodiya said.

The Duke researchers achieved these levels by switching the recipe for the nanoparticles used as catalysts for the reactions to oxidize carbon monoxide in hydrogen-rich gases. Traditional methods of cleaning hydrogen, which are not nearly as efficient as this new approach, also involve gold-iron oxide nanoparticles as the catalyst, the researchers said.

“It had been assumed that the iron oxide nanoparticles were only ‘scaffolds’ holding the gold nanoparticles together, and that the gold was responsible for the chemical reactions,” Sodiya said. “However, we found that increasing the surface area of the iron oxide dramatically increased the catalytic activity of the gold.”

One of the newest approaches to producing renewable energy is the use of biomass-derived alcohol-based sources, such as methanol. When methanol is treated with steam, or reformed, it creates a hydrogen-rich mixture that can be used in fuel cells.

“The main problem with this approach is that it also produces carbon monoxide, which is not only toxic to life, but also quickly damages the catalyst on fuel cell membranes that are crucial to the functioning of a fuel cell,” Hotz said. “It doesn’t take much carbon monoxide to ruin these membranes.”

The researchers ran the reaction for more than 200 hours and found no reduction in the ability of the catalyst to reduce the amount of carbon monoxide in the hydrogen gas.

“The mechanism for this is not exactly understood yet. However, while current thinking is that the size of the gold particles is key, we believe the emphasis of further research should focus on iron oxide’s role in the process,” Shodiya said.

The Duke team’s research was supported by the California Energy Commission and the Oak Ridge Associated Universities.

comments 15

There are fuel cells that can use simple hydrocarbons like methanol directly emitting CO2 and water. Why throw away half of the energy potential by separating the H2 (which is a less energy intensive and much harder fuel to distribute and store)?

The only “green” aspect I see in this is that they are starting with feedstock that should be coming from biomass and therefore is not releasing fossil carbon into the atmosphere.

This is a dumb idea. The purpose shouldn’t be only to produce hydrogen, it should be to make the most efficient use of all the energy potential in the fuel. I’m sorry to see government money going to support foolishness like this.

You are correct that there are fuel cells that directly use simpler hydrocarbons (e.g., solid oxide fuel cells), However, these are high-temperature systems that take a while to start, and they are heavy compared to proton exchange membrane fuel cells. Thus, SOFC are more appropriate in stationary power applications and PEM look better for transportation applications. Both of these applications are important in our overall use of energy, but they have different requirements for hydrogen purity.

We need to think a bit about the criteria that should be used in comparing energy conversion technologies, and it is not always the case that one technology will be better than another technology in every criterion. Greenness is only one criterion. Cost-effectiveness is another, Manufacturability, maintainability, durability, efficiency, infrastructure requirements, safety, size, weight, ability to follow transients, … There are a lot of potential requirements. I would argue that while green is a good goal, it is only one goal, and it may be necessary to take several more steps without factoring green into the mix before the technology evolves to the point that green can become a dominant criterion.

SOFC are useful for combined heat and power generation at +90% efficiency. In winter conditions an EV needs heating for the passenger compartment and batteries. That heat can be recovered from SOFC waste.

SOFC weigh too much for use in passenger vehicles. They might be useful in applications such as locomotives. I do not know how well they could respond to rapid changes in load (typical of the passenger vehicle driving cycle).

How much is too much? Lilliputian Systems makes 2.5W SOFC with 55000mW replaceable butane cartridge . The whole system takes up about 150cc and weights ~200g. Also lots of countries have a winter season where heating is essential for passenger comfort in EVs. To deal with that problem Volvo uses separate ethanol heater. Why not burn that ethanol in SOFC and utalize +90 of the fuel energy.

So 150 hp is about 112,000 watts. You would need 44,800 of those little buggers and at 200 grams each, the total would weigh 8960 kg (~ 9 metric tons). Even with a good savings for repackaging in the appropriate size, the weight is prohibitive. The cost is worse.

Please please please – tell me the requirements of the entire process before telling me that it is a) more efficient or b) more environmentally friendly. In small amounts maybe this is good but HOW DOES IT SCALE.?! Gold & iron, hmmm, mining. Creating nanoparticle combinations of same, chemical process involving what chemicals?
I’m with NegativeNancy – nothing yet as efficient or environmentally friendly as just burning it.

I am missing something here. My thought was similar to negativeNancy’s. Why produce CO2? Why not split water into H and O2 using a green energy (like solar) and then burn the H to get that energy back in a motor or cell?

You produce CO2 because the source of the hydrogen is a hydrocarbon rather than water. Electrolysis of water to produce hydrogen requires more energy than the energy content of the resulting hydrogen. Really bad idea from an economic standpoint. Steam reforming hydrocarbons to produce hydrogen, on the other hand slightly reduces the energy content of the fuel, and produces CO2 as a byproduct.

Thanks, Chuck. I see your point. I do understand how fuel cells work and that, in essence, burning a fuel that has already been produced (wood, oil, biomass) yields more energy and chemistry than starting from scratch with something like solar power and water. I guess I just reacted, maybe, because the word “green” implies environmentally friendly and low or no CO2. I mean, you can consume coal or biomass to get energy (in this case, in the form of hydrogen in the tank) and store it. But then you really can’t say when you use it that you are being a fully “green” user when the production process was not all that green.

What we need, of course, is a free source of power that is green – solar, fusion, current nuclear maybe less so. Then, if we want hydrogen, we simply make it (losing a little of that “free” energy in the form of heat in the process). The economics of it becomes a factor when the energy needed is not “free.”

Funny. When I was working on a fuel cells for transportation project in the 1990s involving steam reforming of methanol, we removed the excess CO using a supported Pt catalyst in a reactor called a PROX (preferential oxidizer). The trick was to preferentially oxidize CO in the presence of a large amount of H2. Using a Langmuir-Hinschelwood mechanism, I showed that injection of steam into the PROX should be effective in preferentially oxidizing the CO and in providing additional moisture needed in the fuel cell anode to keep the proton exchange membrane wet. Subsequent experiments confirmed the predicted lowering of CO.

I guess this isn’t surprising given that the oxidation of hydrogen using water results in water and hydrogen, whereas oxidation of the CO results in CO2 and more hydrogen.

I wonder if the iron oxide provides oxygen to the CO (in which case, it is a reactant and not a catalyst). The article provides no information about the oxidant used in the Duke experiments.